Add cargo:rustc-link-arg to pass custom linker arguments

It is useful to produce correct cdylibs on platforms such as Linux and
MacOS.

Author: lu-zero

src/cargo/core/compiler/build_context/mod.rs

@@ -227,6 +227,7 @@ impl TargetConfig {
             let mut output = BuildOutput {
                 library_paths: Vec::new(),
                 library_links: Vec::new(),
+                linker_args: Vec::new(),
                 cfgs: Vec::new(),
                 env: Vec::new(),
                 metadata: Vec::new(),
@@ -262,6 +263,12 @@ impl TargetConfig {
                             .library_paths
                             .extend(list.iter().map(|v| PathBuf::from(&v.0)));
                     }
+                    "rustc-link-arg" => {
+                        let args = value.list(k)?;
+                        output
+                            .linker_args
+                            .extend(args.iter().map(|v| v.0.clone()));
+                    }
                     "rustc-cfg" => {
                         let list = value.list(k)?;
                         output.cfgs.extend(list.iter().map(|v| v.0.clone()));

src/cargo/core/compiler/custom_build.rs

@@ -21,6 +21,8 @@ pub struct BuildOutput {
     pub library_paths: Vec<PathBuf>,
     /// Names and link kinds of libraries, suitable for the `-l` flag
     pub library_links: Vec<String>,
+    /// Linker arguments suitable to be passed to `-C link-arg=<args>`
+    pub linker_args: Vec<String>,
     /// Various `--cfg` flags to pass to the compiler
     pub cfgs: Vec<String>,
     /// Additional environment variables to run the compiler with.
@@ -425,6 +427,7 @@ impl BuildOutput {
     ) -> CargoResult<BuildOutput> {
         let mut library_paths = Vec::new();
         let mut library_links = Vec::new();
+        let mut linker_args = Vec::new();
         let mut cfgs = Vec::new();
         let mut env = Vec::new();
         let mut metadata = Vec::new();
@@ -472,6 +475,7 @@ impl BuildOutput {
                 }
                 "rustc-link-lib" => library_links.push(value.to_string()),
                 "rustc-link-search" => library_paths.push(PathBuf::from(value)),
+                "rustc-link-arg" => linker_args.push(value.to_string()),
                 "rustc-cfg" => cfgs.push(value.to_string()),
                 "rustc-env" => env.push(BuildOutput::parse_rustc_env(&value, &whence)?),
                 "warning" => warnings.push(value.to_string()),
@@ -484,6 +488,7 @@ impl BuildOutput {
         Ok(BuildOutput {
             library_paths,
             library_links,
+            linker_args,
             cfgs,
             env,
             metadata,

src/cargo/core/compiler/mod.rs

@@ -365,6 +365,10 @@ fn rustc<'a, 'cfg>(
                         rustc.arg("-l").arg(name);
                     }
                 }
+                for arg in output.linker_args.iter() {
+                    let link_arg = format!("link-arg={}", arg);
+                    rustc.arg("-C").arg(link_arg);
+                }
             }
         }
         Ok(())